dimensionless quantity
quantity with no physical dimension
probability
measure of the expectation that an event will occur or a statement is true
relative atomic mass
dimensionless physical quantity: ratio of the average mass of atoms of an element to one unified atomic mass unit
view factor
proportion in thermal radiation
mixing ratio
abundance of one component of a mixture relative to others
valence
measure of an element's combining capacity with other atoms when it forms chemical compounds or molecules
scale
ratio of a distance on the map to the corresponding distance on the ground
Boltzmann factor
probability measure that gives the probability that a system will be in a certain state
ion transport number
fraction of electrical current carried by given ionic species
heat capacity ratio
thermodynamic ratio of isobaric to isochoric specific heat capacities
porosity
ratio of void volume and total volume of a porous material
alcohol by volume
measure of how much alcohol is in a beverage
activity coefficient
value accounting for thermodynamic non-ideality of mixtures
compression ratio
ratio of the volume of a combustion chamber from its largest capacity to its smallest capacity
cloud cover
fraction of the sky obscured by clouds when observed from a particular location
numerical aperture
dimensionless number that characterizes the range of angles over which the system can accept or emit light
spectral luminous efficiency
spectral sensitivity of human visual perception of brightness
Hatta number
dimensionless parameter that compares the rate of reaction in a liquid film to the rate of diffusion through the film
Beale number
parameter that characterizes the performance of Stirling engines
kinetic friction factor
ratio of the force component in the direction of motion to the contact force of a sliding body
refractivity
the refractive index minus one
apparent magnitude
measure of brightness for celestial objects, as seen from Earth
isotopic signature
characteristic set of ratios of stable or unstable isotopes
crop factor
multiplier factor in digital imaging, compared to 35mm film camera focal length
sun protection factor
measure of the fraction of sunburn-producing ultraviolet rays that reach the skin
aspect ratio
ratio of an aircraft's wing span to its mean chord
air changes per hour
measure of the air volume added to or removed from a space
net tonnage
ship cargo space volume
luminosity distance
astronomical measurand
quality factor
factor taking into account health effects in the determination of the dose equivalent
tortuosity
Parameter for diffusion and fluid flow in porous media
relative humidity
ratio of the partial pressure of water vapor in humid air to the equilibrium vapor pressure of water at a given temperature
quantum yield
number of times a specific event occurs per photon absorbed by the system
fudge factor
ad hoc element introduced into a calculation
reactivity
measure of the criticality of a nuclear chain reacting material
radiant efficiency
energy conversion in optics
relative density
ratio of the density (mass per volume) of a substance to the density of a given reference material
relative permeability
ratio of permeability to the magnetic constant
stoichiometric coefficient
absolute value of the stoichiometric number
color rendering index
measure of the ability of a light source to reproduce the colors in comparison with an ideal or natural light source
solid angle
measure of a subtended portion of a sphere, used to describe the apparent size of items in a three-dimensional field of view
partition function
function in thermodynamics and statistical physics
prevalence
number of disease cases in a given population at a specific time